Process for producing ferrosilicon



United States Patent 2,776,885 PROCESS FOR PRODUCING FERROSILICON Sieds Koopal, Sittard, and Pierre L. S rnit and Willem van Loon, Gcleen, Netherlands, assignors to Stamicarbon N. V., Heerlen, Netherlands.

NoDrawing. Application January 4, 1954-,

' Serial No. 402,134

Claims priority, application Netherlands January 6, 1953 8 Claims. (cl. 75*133-5) containing iron slag ancla calcareous flux, is continuously fed into a shaft furnace at the top thereof, and a preheated air blast is injected into the lower part of the furnace, whereby the amount of heat and the; high temperature. needed for the formation of ferrosilicon is generated by burning part of the fuel and the reduction of the iron oxide and silica is eflected by the remaining. part of the fuel. (As a result molten ferrosilicon and a liquid. slag, formed by the calcareous fluxand the ashforming constituents of the charged materials are discharged from thelower part of the furnace. In this manner only a low grade ferrosilicon with not more than 18% Si can be obtained.

Though it has been expected that by increasing the oxygen content of the blast and by using an oxygen enriched air, blast, a ferrosilicon containing a higher Si-content would result, attempts toproduce a high' grade ferrosilicon in this manner have been unsuccessful hitherto. However, in technical practice ferrosilicon of higher Si-content, for example higher than 25% is in great demand; up to now these alloys of high Si percentages have only been prepared in electric furnaces, in which process an electric current is passed through a bed consisting of a mixture of iron, coke and silica. In order to arrive at a workable process in this case the ash content of the coke must be kept low, while also the silicaemployed has to satisfy rather rigid requirements as regards its purity.

As a rule the silica has to be supplied in the form of pure In this manner the silicon content of the ferroquartz. silicon can be increased to a high value, even to 95-99%.

This preparation in electric furnaces is costly owing to the large consumption of electric current needed. Another drawback is the fact that the inflammable gases formed during this reduction process find but little technical application, since they are difiicult to recover and the amount is relatively small.

Objects The principal object of the present invention is the provision of a novel procedure for preparing high grade ferrosilicon, having 2555% Si, without using costly electric current.

Other objects include:

(a) The provision of an improved procedure for the preparation of high grade ferrosilicon in a blast furnace;

(b) The provision of an improved procedure for the preparation of high grade ferrosilicon in a blast furnace and the simultaneous withdrawal from the furnace of a gas which has excellent properties for heating purposes and contains but a minor content of nitrogen. The gas 2,775,885 Patented Jan. 8, 1957 2 may also be used as starting material in organic syntheses; (c) The provision of an improved procedure for the preparation of high grade ferrosilicon in a blast furnace by applying an oxygen containing blast of such composition, that a sudden rise or fall of the temperature in the hearth of the furnace can be regulated in a rapid manner by changing the composition of the blast.

Still further objects and the entire scope of applicability of the present invention will become apparent from the detailed description given hereinafter.

Description The objects briefly outlined above are realized in accordance with the present invention by blowing into the hearth of the blast furnace an oxygen containing blast consisting of a mixture of oxygen and an endothermic gasifying agent such as steam and/ or carbon dioxide, in which mixture the oxygen content amounts to at least 65% by vol. and does not exceed 90% by vol. In practice tonnage-oxygen i. e., industrial oxygen contaminated with nitrogen and containing 9095 vol. percent of oxygen with the rest nitrogen, is used, the nitrogen present in the tonnage-oxygen having no adverse eifect. In manufacturing ferrosilicon of at least 25% Si, 21 high tempera ture for instance 2200" 'C. or more, is needed in the hearth of the furnace. Such a temperature can be generated by applying a steam and/ or carbon dioxide-oxygen mixture containing at least 65% by vol. of oxygen. The oxygen content of the blast must further be adapted to the silica content of the charge; the silicon content in the ferrosilicon to be produced is dependent on the ratio silica-iron in the charge; the ferrosilicon-gas ratio is es-- pecially influenced by the amount of fuel in the charge.

In view of the simultaneous production of well-balanced amounts offerrosilicon and gas, it is preferred to use a blast containing -85% by vol. of oxygen and then to compose the charge so that per 1000 m? (N. P. T.) gas with a calorific value of about 2800 kg./cals. about 400 kg. of ferrosilicon of 25% Si or about 200 kg. of ferrosilicon of 55% Si or a proportionate amount of ferrosilicon of a silicon content lying between 25 and 55% will be produced.

Oxygen percentages higher than by vol. have to be avoided, since otherwise unduly high temperatures might be produced in the hearth of the furnace. For, theseundulyhigh temperatures would cause an excessive evaporation of the silica whereby this silica sublirnates at colder places in the shaft, as a result of which the charge might get stuck or stoppages might occur.

It has also been found necessary for the same reason to keep the content of ash forming constituents in the charge relatively low. The ash content of the fuel should not exceed 10% and preferably the silica applied should contain at least 90% SiOz.

Owing to the use of starting materials containing few ash-forming constituents no liquid slag need be withdrawn from the furnace, the slag-forming components are evaporated and removed together with the gases escaping at the top of the furnace.

The endothermic gasifying agent present in the blast makes it possible to maintain the most favourable reaction temperature, and in the event of a sudden rise or fall of the temperature in the hearth to vary the oxygen content of the blast, without influencing the quality of the gas produced.

The manner in which the present process will be carried out and the operational details thereof can be more fully comprehended by reference to the following illustrative examples of actual operations in accordance with the invention.

Examples EXAMPLE I A shaft furnace was fed with a charge consisting of a mixture of 100 parts by weight of coke, parts by weight of ironand 33.5 parts by weight of silica gravel. The coke had an ash percentage of 10%; the gravel contained 96% of SiOz. The blast used was a mixture of tonnage oxygen and steam having the following composition:

26.5% by vol. H2O 67.0% by vol. 02 6.5% by vol. of N2 EXAMPLE II A shaft furnace was filled with a charge consisting of a mixture of 100 parts by weight of coke (ash content.

10%), 11 parts by weight of iron and 39.5 parts by weight of gravel (96% SiOz).

The gasifying agent used was a mixture of technical oxygen and carbon dioxide of the following composition:

19% by vol. of CO2 73.5% by vol. of 02 7.5% by vol. of N2 The ferrosilicon formed had a silicon content of 51%.

i The calorific value of the final gas was 2900 kg./cals. per

m. (N. P. T.).

The production of ferrosilicon per 1000 m. (N; P. T.) gas amounted to 86 kg.

EXAMPLE III The charge supplied to the shaft-furnace was composed of 100 parts by weight of coke, 19 parts by weight of iron and 77 parts by weight of silica gravel.

The blast used was a mixture of tonnage oxygen and steam having the following composition:

83% by vol. of 02 6.5 by vol. of N2 10% by vol. of H20 The ferrosilicon produced contained 52% silicon and the production amounted to 182 kg. ferrosilicon per 1000 m. (N. P. T.) gas with a calorific value of 2600 kcaL/m. (N. P. T.).

4 Summary As will be appreciated from the foregoing, the present invention provides a new and highly advantageous process for the production of high grade ferrosilicon and, simultaneously, the production of a gas mixture of excellent heating value and such a valuable composition that, if desired, it can be used for organic syntheses.

Using an oxygen containing blast consisting of an oxygen-steam mixture, an oxygen-carbon dioxide mixture or an oxygen-steam-carbon dioxide mixture, it is possible, by varying the composition of the blast, to maintain and to regulate the proper reaction temperature, which may be in the range of 22003000 C., in the hearth of the furnace at difierent compositions of the charge.

Consequently, the ratio between the amounts. of gas and ferrosilicon to be produced may be varied at will.

We claim:

1. In a process for producing ferrosilicon by heat reacting a mixture of fuel which is primarily carbon, silica and a member of the group consisting of iron and iron oxide in the presence of an oxygen-containing blast, the improvement whereby ferrosilicon containing 25-55% silicon and desirable inflammable gases are obtained, said improvement comprising utilizing, as said oxygen-containing blast, a gaseous mixture consisting essentially of -90% by volume oxygen and at least one member of the group consisting of steam and carbon dioxide.

2. The process of claim 1 wherein said gaseous mixture contains -85% by volume of oxygen.

3. The process of claim 1 wherein the ash content of said fuel does not exceed 10% by weight.

4. The process of claim 1 wherein the reaction temperature is kept within the range of 2200-3000 C.

5. The process of claim 1 wherein said gaseous mixture includes both steam and carbon dioxide.

6. The process of claim 1 wherein said gaseous mixture includes only one member of the group consisting of steam and carbon dioxide.

7. The process of claim 1 wherein said gaseous mixture includes nitrogen.

8. The process of claim 1 wherein the oxygen in said gaseous mixture is tonnage-oxygen consisting essentially of -95% oxygen and 105% nitrogen.

. References Cited in the file of this patent UNITED STATES PATENTS 1,231,260 Johnson June 26, 1917 2,593,257 Bradley et a1. Apr. 15, 1952 FOREIGN PATENTS 442,478 Great Britain Feb. 10, 1936 

1. IN A PROCESS FOR PRODUCING FERROSILICION BY HEAT REACTING A MIXTURE OF FUEL WHICH IS PRIMARILY CARBON, SILICA AND A MEMBER OF THE GROUP CONSISTING OF IRON AND IRON OXIDE IN THE PRESENCE OF AN OXYGEN-CONTAINING BLAST, THE IMPROVEMENT WHEREBY FERROLILICON CONTAINING 25-55% SILICON AND DESIRABLE INFLAMMABLE GASES ARE OBTAINED, SAID IMPROVEMENT COMPRISING UTILIZING, AS SAID OXYGEN-CONTAINING BLAST, A GASEOUS MIXTURE CONSISTING ESSENTIALLY OF 65-90% BY VOLUME OXYGEN AND AT LEAST ONE MEMBER OF THE GROUP CONSISTING OF STEAM AND CARBON DIOXIDE. 